In the underground excavation industry, there are presently instruments to measure the deformation of tunnel walls in order rationally to establish underground support requirements as a tunnel is being dug, for a mine, for example. By measuring rock deflection at the tunnel wall, it is possible to predict tunnel support requirements as tunnel digging progresses. To be most beneficial, it is necessary to measure the rock deflection that occurs as the supporting tunnel rock is being removed. Such a requirement implies measuring the tunnel rock deflection at a location very close to the digging space of the tunnel.
It is known that rock deflection can be measured by forming a radial bore in the tunnel and inserting a rod-like measuring instrument into the bore. One end of the instrument is anchored to the end of the bore remote from the tunnel wall, while the other end of the instrument is anchored to the end of the bore adjacent the tunnel wall. The two ends of the instrument are movable relative to each other, whereby deflection of the rock is determined by measuring the relative displacement between the two ends of the instrument.
The prior art instruments have generally required connections to external signal storage devices, such as recorders, as well as to power supplies for transducers mounted on the instrument for measuring the relative movement of the two ends of the rod-like instrument. However, such external connections cannot usually be properly established and maintained, without greatly impeding the progress of the tunnel as it is being dug. Hence, the typical prior art instruments have not been compatible with measuring rock deflection as the tunnel is being dug, and thereby have not been effectively utilized in predicting tunnel support requirements as tunnel digging progresses.
It is, accordingly, an object of the present invention to provide a new and improved instrument for measuring the amount of deflection of a subterranean tunnel while the tunnel is being dug.
Yet another object of the invention is to provide a new and improved signal storage apparatus, in the form of a paper tape recorder, that can be contained on an instrument used to measure the amount of deflection of a subterranean tunnel, and which instrument is adapted to be inserted into a relatively small diameter bore extending radially from the tunnel wall.